Posted October 11, 2022

Kathleen M. Sakamoto, M.D., Ph.D., Stanford University

Diamond-Blackfan anemia (DBA) is an inherited bone marrow-failure syndrome characterized by defects in erythropoiesis (red blood cell development deficiency), congenital abnormalities, and a vulnerability to cancer. Current treatment options are not ideal, as they often present with serious side effects. For example, most patients with DBA develop anemia during early childhood and often require blood transfusions, resulting in iron overload and, eventually, organ damage. Therefore, there is a need for greater understanding of the mechanistic pathways involved in DBA pathogenesis as they may identify targets that can be exploited therapeutically for improved patient care.

It has been noted more than 75% of DBA patients have mutations in ribosomal subunits, with about 25% having mutations in small subunit ribosomal protein 19 (RPS19). These mutations cause haploinsufficiency, or insufficient amounts of RPS19, contributing to failures of erythropoiesis. Having identified Nemo-like kinase (NLK) as being hyperactive in bone marrow progenitor cells with RPS19 haploinsufficiency,¹ Dr. Sakamoto's team hypothesized that NLK could be contributing to anemia in DBA. With support from a Fiscal Year 2018 Bone Marrow Failure Research Program Idea Development Award, Dr. Sakamoto and her team initiated innovative studies interrogating the effects of NLK inhibition on erythropoiesis in models of DBA.

Under this award, the Sakamoto laboratory and collaborators investigated NLK-associated pathways with the goal of characterizing existing inhibitor candidate response, and identifying additional therapeutic targets, using techniques such as qRT-PCR, lentiviral transduction, flow cytometry, cloning, and CRISPR/Cas9 gene editing in DBA models. The team found that SD208, an inhibitor of NLK, activated the mammalian target of rapamycin (mTOR) pathway and increased translational efficiency. mTOR plays a vital part in cell-growth regulation, protein synthesis, and other processes. When NLK inhibition was combined with leucine, a crucial amino acid utilized during protein biosynthesis, the mTOR activity increased by an additional 50%, and an 8-fold increase of erythroid progenitor cells was observed.² Building on the knowledge base that inhibition of NLK activity and suppression of NLK expression boosts erythroid expansion, the investigators tested Metformin (an approved type 2 diabetes medication) in human cell lines and zebrafish DBA models. Results revealed an increase in numbers of erythroid progenitor cells through induction of MiR-26a (a microRNA regulator of gene expression).³

Results from the BMFRP-funded interrogation of the NLK signaling pathways has allowed for further exploration of compounds that suppress NLK and increase erythropoiesis in cells with ribosomal insufficiency. The team reported the active agent for ginseng, Rb1, also inhibits NLK expression and increases erythropoiesis through expression of miR-208.⁴ The Sakamoto laboratory is currently examining additional potential drugs for future treatment of DBA patients.

Research discoveries into the mechanisms involved in NLK inhibition and erythropoiesis expansion, such as Dr. Sakamoto's, promote a greater understanding of DBA pathogenesis, which is beneficial in advancing the cause of identifying additional therapeutic targets and facilitating better treatment options. New treatment approaches bring the potential of reducing the negative side effects of current treatments and could improve the quality of life for patients living with DBA.

Links:

Public and Technical Abstracts: The Role of Nemolike Kinase in the Pathogenesis and Treatment of Diamond-Blackfan Anemia

Publications:

¹Wilkes MC, Shibuya A, and Sakamoto KM. 2021. Signaling pathways that regulate normal and aberrant red blood cell development. Genes (Basel). Oct 19;12(10):1646. doi: 10.3390/genes12101646

²Wilkes MC, Siva K, Chen J, et al. 2020. Diamond Blackfan anemia is mediated by hyperactive Nemo-like kinase. Nat Commun. Jul 3;11(1):3344. doi: 10.1038/s41467-020-17100-z

³Wilkes MC, Siva K, Varetti G, et al. 2020. Metformin-induced suppression of Nemo-like kinase improves erythropoiesis in preclinical models of Diamond-Blackfan anemia through induction of miR-26a. Exp Hematol. Nov;91:65-77. doi: 10.1016/j.exphem.2020.09.187

⁴Wilkes MC, Jung K, Lee BE, et al. 2021. The active component of ginseng, ginsenoside Rb1, improves erythropoiesis in models of Diamond-Blackfan anemia by targeting Nemo-like kinase. J Biol Chem. Sep;297(3):100988. doi: 10.1016/j.jbc.2021.100988

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